Because 1,3-propanediol (1,3-PDO) is a raw material of a polyester fiber of high quality, which includes polytrimethylene terephthalate (PTT), the demand is increasing in recent years. As one process for synthesis of 1,3-propanediol, there is an acrolein hydration and hydrogenation process shown in Non-Patent Literature 1. This process is a production method involving subjecting acrolein which has been obtained by oxidizing propylene that is a crude oil material with air in the presence of a catalyst, to a hydration/hydrogenation reaction, and is established as an industrial production method. However, it has been desired in recent years to develop a process for synthesis of 1,3-propanediol from a biological raw material, on the background of a remarkable rise of a crude oil price.
A process for synthesis of 1,3-propanediol from a biological raw material with a chemical synthesis process is not reported, but technologies for synthesizing acrolein which is a precursor exist, and one of the technologies is described in Non-Patent Literature 2. This process is a process for synthesis of acrolein by using glycerol which is a biological raw material as a starting material, and using a supercritical water of 400° C. at 35 MPa. The process has a feature in the point that a proton originating from a trace quantity of sulfuric acid added into the supercritical water has an effect of increasing a generation amount of active hydrogen ions which trigger the dehydration reaction of glycerol in supercritical water, and functions as a co-catalyst for accelerating the progress of the reaction. However, in Non-Patent Literature 2, the concentration of glycerol in a raw material is as extremely low as about 1%, but on the other hand, much energy is consumed for raising the temperature and pressure of water when producing the supercritical water. Accordingly, there has been a problem that the utilization efficiency for energy is extremely poor in consideration of commercial production.
In contrast to this, in Non-Patent Literature 3, optimum conditions on a reaction time and the concentration of sulfuric acid which is a co-catalyst have been derived, a reaction experiment has been carried out under a condition in which the concentration of glycerol has been increased to 15% by weight, and a reaction yield exceeding 70% has been attained. Thereby, energy efficiency is improved, but in order to structure a process having market competitiveness, the running cost needs to be reduced by increasing the concentration of glycerol to the limit. On the other hand, as the concentration of glycerol increases, the amount of produced reaction by-products such as tar and a carbon particle increases. Then, the by-product adheres to a valve element and a valve seat of a valve, thereby the valve element and the valve seat are abraded, the operation range of the valve element is restricted, and it may become difficult to precisely control the pressure. If the operation is further continued, the by-product causes blockage in narrow portions such as a pipe, the valve and a filter, and it may become difficult to operate the plant. The reason is because the carbon particles coagulate and grow due to the adhesiveness of tar. In Non-Patent Literature 3, such problems are not studied.
The technology in Patent Literature 1 relates to a method for producing acrolein, which includes at least steps of: (a) obtaining an aqueous acrolein reaction phase at least one part of which is in a supercritical region, by supplying an aqueous glycerol phase to an acrolein reaction region; (b) removing acrolein from the above described acrolein reaction phase, and obtaining an acrolein phase and an acrolein reaction phase in which the concentration has been reduced; and (c) resupplying at least one part of the acrolein reaction phase in which the concentration has been reduced, to the acrolein reaction region. Patent Literature 1 discloses that the acrolein reaction region preferably contains a dehydration catalyst other than water, that the dehydration catalyst is a compound except water, which has acidity and also acts as a strong acid in a region near the supercritical region or in the supercritical region, that the glycerol phase contains less than 10% by weight of, particularly preferably less than 8% by weight of and most preferably less than 6% by weight of glycerol with respect to the total amount of the glycerol phase, that the least amount of glycerol in the glycerol phase is preferably 0.01% by weight, particularly preferably is 0.1% by weight and most preferably is 1% by weight, and the like. However, in the present Literature, the concentration less than 10% by weight of glycerol is a value in which a sufficient utilization efficiency of energy is not necessarily obtained, and measures against the tar and the carbon particle are not studied. Accordingly, the commercialization of the method is difficult.
The technology in Patent Literature 2 relates to a method for producing acroleins, which includes using a supercritical fluid or a subcritical fluid in a high-temperature and high-pressure state as a reaction solvent, and selectively synthesizing acroleins by one stage of a synthesis reaction from glycerols under the condition of using no catalyst or a trace quantity of a catalyst, in a process for synthesis of acroleins. Patent Literature 2 discloses to use a supercritical fluid or a subcritical fluid in a high-temperature and high-pressure state as a reaction solvent, to use water in a supercritical or subcritical state as the supercritical fluid or the subcritical fluid, to use an inorganic acid as a trace quantity of a catalyst, to use an aqueous solution in which a trace quantity of a catalyst has been added to an aqueous solution of glycerols, as a raw material, and to subject the aqueous solution to a reaction. However, under conditions with no catalyst, at a temperature of 350° C. or lower and with a pressure of 22 MPa or less in the present literature, an amount of generated active hydrogen ions (having catalysis action), which should act on glycerol, is small, and the reaction becomes extremely slow. For this reason, the influence of the conversion of a reactant to tar or carbon particles due to a thermal decomposition reaction which is a side reaction becomes large, and such problems are caused that the a yield of a raw material decreases and a blockage occurs in a pipe. The measures against the problems are not also studied.
The technology in Patent Literature 3 relates to a catalyst which is preferably used when acrolein or an aqueous solution of acrolein is produced by volatilizing an aqueous solution of glycerol and using a dehydration reaction in a gaseous phase using a solid catalyst, and to a method for producing acrolein using the catalyst. Patent Literature 3 describes that the glycerol of a raw material may contain also 0 to 95% by weight of an inactive condensable substance such as water, that a solvent or the like may also exist which is not involved in the reaction, and that the concentration of the glycerol of the raw material is preferably 5 to 100% by weight. However, in the present method, by-products such as tar and carbon particles are produced and if the by-products cover the interface of a catalyst, the reactivity is remarkably lowered. For this reason, catalyst regeneration treatment is frequently needed, a plant operation becomes complicated, and besides a catalyst performance is lowered by the aggregation of carried precious-metal particles along with a regeneration operation which is ordinarily heat treatment, which becomes a problem that is difficult to be solved.